1. Field of the Invention
This invention relates to a coated fertilizer capable of controlling its dissolution-out velocity. More particularly, it relates to a coated fertilizer which begins to dissolve out after lapse of a definite period after its application to exhibit its fertilizing effect.
The product of the present invention is obtained by coating a granular fertilizer with a coating having a powder of a sugar polymer or its derivative dispersed therein.
2. Description of the Related Art
In recent years, a coated granular fertilizer having a granular fertilizer capsulated to control the dissolution-out velocity of its fertilizing effect component has been developed and gradually practically used. Such a coating process for the coated granular fertilizer is roughly classified into the following two kinds: 1 a relatively thick coating is carried out using a coating material such as sulfur, wax, a low molecular weight polymer such as a low molecular polyolefin, etc. and 2 a relatively thin coating is carried out using a high molecular weight material such as polyolefin, etc.
However, as to such coated granular fertilizers, the product obtained by coating with the latter, high molecular weight material, is superior in that the controllability of the dissolution-out velocity is higher, the damage of the coating at the time of handling the granular fertilizer is smaller, etc. On the other hand, however, the product (coated granular fertilizer) has the drawbacks that the coating process with the high molecular weight material is technically not easy; a relatively long time is required for decomposing the coating residue remaining in soil after its application; etc.
The present inventors previously have developed techniques of coating granular fertilizers with a high molecular weight material and controlling the dissolution-out velocity of a component having a fertilizing effect, and have applied for patents. For example, we have disclosed a coating technique with a polyolefin resin solution (Japanese patent publication No. Sho 50-99,858) and a high level technique of controlling the dissolution-out velocity by the simultaneous use of a polyolefin resin, an ethylene-vinyl acetate copolymer and a surfactant (Japanese patent publication No. Sho 60-37,074).
Further, we have disclosed a technique that by using a product obtained by further mixing and dispersing powder of a mineral material such as talc, etc. or sulfur in a polyolefin resin composition as described above, not only the dissolution-out velocity of a component having a fertilizing effect can be controlled, but also collapse or decomposition of the remaining capsule i.e. a coating residue after use of the granular fertilizer (its application onto soil) can be promoted (Japanese patent publication No. Sho 60-3,040 and Japanese patent application laid-open No. Sho 55-1,672).
These techniques for controlling the dissolution-out refer basically to a technique for controlling the dissolution-out period, and in other words, refer to a technique for controlling the dissolution-out velocity, expressing the quantity dissolved out per period or per hour. According to these techniques, a commodity optionally affording a desired fertilizing effect over a short or long period has been provided, and an evolutional agricultural technique of cultivation with totally a basal fertilizer, etc. has been established.
However, in order to improve these techniques to a technique on a higher level, a fertilizer of such a type that a desired dissolution-out begins after lapse of a definite period, has been desired. (Problem to Be Solved by the Invention)
The present inventors have made extensive research in order to make the above-mentioned technique of optionally controlling the dissolution-out velocity, disclosed by the present inventors, correspond to a new technique on a higher level, of dissolution-out after lapse of a definite period after its application, which technique has been earnestly desired by farmers and agricultural engineers, that is, a technique of the so-called time limit dissolution-out control type. As a result, we have found that when a sugar polymer or its derivative is dispersed in the coating of fertilizer, it is possible to control the induction period before start of dissolution-out and the duration of dissolution-out after start of dissolution-out, and we have completed the present invention.
As apparent from the foregoing, the object of the present invention is to provide a fertilizer which can optionally and independently control the dissolution-out-induction period since its application until the start of dissolution-out and the dissolution-out period since the start of dissolution-out till completion of dissolution-out.
Further, according to the present invention, it is also possible to provide a fertilizer whose capsule decomposes or collapses after completion of dissolution-out, bY choosing a known coating material having a decomposition or collapse function.